The present invention relates to a warning sound generating device, and especially to an emergency warning siren device for a fire alarm.
As prior art of the present invention, the following documents may be cited: U.S. Pat. No. 4,310,833, U.K. Pat. No. 2,145,905B, U.K. Pat. No. 2,094,099A, U.K. Pat. No. 2,073,541B, U.K. Pat. No. 1,480,414, U.K. Pat. No. 566,398, U.K. Pat. No. 430,025, and Elements of Acoustical Engineering-Olson (D. Van Nostrand Co. Inc.) 2nd Edition Reprinted, March 1949 (See page 211, FIG. 7.21).
U.K. Pat. No. 2,145,905B discloses an electric siren. The siren comprises a base mounted on a sound generating means, and a plurality of horn members disposed coaxially and attached to the base. The horn members opening forward and another horn member opening backward (toward the base) are radially alternatingly disposed on the base. Consequently, a folded and broadening sound passageway are defined by the horn members. With such a construction, the generated sound spreads widely and is broadcast over a long distance. Since the sound passageway is folded, if the length of the whole siren is short, a long sound passageway can be provided.
However, in the production of the siren, a plurality of the horn members are mounted on the base one by one, and therefore the efficiency of assembly is not improved.
In addition, the structure is such that the horn member opening backward may not be stably supported by the base, so that the horn member is of inferior strength.
Furthermore, it is considered to be difficult to make the entire siren compact and to make the sound passageway long if the number of folds is kept constant.